Digital Signal Processing: A Practical Guide (Part 1)

This book is intended for those who work in or provide components for industries that use digital signal processing (DSP). There is a wide variety of industries that utilize this technology. While the engineers who implement applications using DSP must be very familiar with the technology, there are many others who can benefit from a basic knowledge of its' fundamental principals, which is the goal of this book—to provide a basic tutorial on DSP.

Editor's Note: This extract is Part 1 of a seven-part series from this book.

12 comments

Easy to read, easy to follow, it surely is effective on reminding (some of) us what we learned in school.
Though, I've always questioned why did Nyquist came out with the term “aliasing”, it's not that intuitive to me... perhaps because english isn't my first language but... wouldn't have been better something like a “phantom frequency” or “mirrored signal” or... well... you get what I'm saying right? :-)

I understand exactly what you mean. I approach it differently, when a higher frequency signal shows up as lower frequency signals it is assuming an alias. It is masquerading as a different signal( or signals) and assuming an alias, or as it was called aliasing. It is an alias because the actual signal is there and could be measured, so it is not a phantom, the real signal is still there, just assuming an alias to ruin your day.

When I was at school we called it a "beat frequency", because at AF it "beat time" as you would to music. I wondered for years what "aliasing" meant - I assumed it was something way above my head - until I came across a definition somewhere and realised it was just my old friend "the beat" after all!

Like Luis, I've enjoyed the reminder. I'm actually still going through this course, just a bit at a time.
Back in my grad school days, studying Computer Vision, we applied DSP to graphical signals and the aliasing made sense to a point. But "maxm"'s comment on an alias being a masquerading signal is excellent. Also, Ian's "beat frequency". I'd never thought of two slightly out of tunes strings as a form of sampling before! But it's true! Thanks.

Hi. Ian's notion that spectral aliasing is related to "beat frequency" (the sum of two audio sine waves that are close in frequency) is not correct. What people call "beat frequency" can happen in the analog world (guitar strings) but aliasing can only happen in the worlds of sampled data (digital signals). Aliasing cannot exist with analog signals. By the way, what people call "beat frequency" is actually an audio illusion. When you simultaneously pluck a 400 Hz guitar string and a 410 Hz guitar string, the resultant audio signal contains *NO* spectral energy at 10 Hz. The real story about "beat frequency" can be found at: http://www.dsprelated.com/showarticle/189.php.
[-Rick-]

I am always looking for more DSP resources. The info in the 7-part preview is good in that it introduces a large number of DSP topics and applications and will help to pique the curiosity of readers. However, perhaps by trying to be too broad, it falls short in places. As an introduction, it could serve as a launchpad to more rigorous resources.
Some comments on the first few parts:
- Nyquist should be mentioned for bandlimited signals, not just baseband signals ... but many authors only consider baseband.
- FIR filters do not always have linear phase. e.g., there are minimum- and maximum-phase filters. If your application does not need linear phase (constant group delay) then a linear-phase FIR filter wastes resources.
- Least-squares isn't the only, nor is it often the most important filter design criterion.
- you should always use optimization routines for designing FIR filters and especially when you have limited resources in your DSP chip. You will get a better frequency response and/or lower order than if you simply use windowing functions.
- IIR filters are very useful in DSP! Their use requires more care but the benefits can be huge. e.g., you may be able to get considerably fewer multiply/accumulate operations.
- although sample-rate conversion is useful, the main thrust in full-fledged multirate DSP is to significantly reduce the total amount of computation required for some DSP systems. e.g., it is useful for low bit-rate coding systems, etc.
- It's great to have a book that has good verbal explanations, but more supporting math wouldn't hurt.

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